The present invention provides a coil tube or circuit arrangement for a closed circuit cooling tower. More specifically, a coil tube assembly for a cooling tower, which is usually a counterflow closed-circuit cooling tower, has a coil tube assembly with a plurality of coil circuits. The disclosed method of circuiting the coil assembly for closed-circuit cooling towers gives an enhanced performance, and more particularly enhanced performance for coil assemblies operating at low internal fluid flow.
In a typical coil tube arrangement for a cooling tower, the circuits are provided between an upper header with a fluid inlet nozzle to a lower header with a fluid outlet nozzle. The individual circuits extend from the upper header to the lower header in a serpentine arrangement, which may be generally described as a series of parallel straight tube lengths connected by unshaped bends. Fluid has historically been communicated from the top of the coil tube assembly, or upper header, to the lower header by traversing the plurality of parallel tube lengths.
The fluid to be cooled is circulated inside the tubes of the units heat exchanger. Heat flows from the process fluid through the coil tube wall to the water cascading over the tubes from the spray-water distribution system. Air is forced upward over the coil, evaporating a small percentage of the water, absorbing the latent heat of vaporization and discharging the heat to the atmosphere. The remaining water is recovered in the tower sump for recirculation to the water spray. Water entrained in the air stream is recaptured in mist eliminators at the unit discharge and returned to the sump. It is also known that the water distribution system can be shut off and the unit may be run dry. Air is still forced upward over the coil, but the heat is now solely dissipated to the atmosphere by sensible cooling.
In typical evaporative heat exchangers it has been customary to provide several spray-liquid headers located in superposed relation spanning a bank of tubes carrying a fluid to be cooled. A plurality of smaller tubes or branches extend laterally from the headers, with each branch containing one or more nozzles which emit spray patterns impinging on the fluid carrying tubes.
U.S. Pat. No. 4,196,157 to Schinner teaches a separation arrangement between the adjacent tubes of a coil assembly. In addition, the structural arrangement of a typical closed-circuit cooling tower structure is noted in the text. The typical feed arrangement for the fluid to be cooled is taught and illustrated in this patent with an upper and inlet manifold for receipt of warm fluid for cooling, a lower and outlet manifold for discharge of cooler fluid, and the connection of the serpentine tube assembly therebetween coupling the inlet and outlet manifold. This is an exemplary teaching of the understanding of heat transfer and maximum expected cooling for closed-circuit cooling towers in the prior art.
The preservation of the cooling coil layout has been almost uniformly practiced by the industry as a whole. The direction of fluid flow through the coils or circuits was considered a reflection of a tenet of practice in the closed-circuit cooling tower art. That is, maximum cooling of the fluid would be realized by maintaining the fluid within the tubes counterflowing against the direction of air flow. However, recent developments have noted a spray-water cooling effect, that has heretofore not been taken into account.
The present invention provides means for recovering the plenum-area, spray-water cooling effect between about the bottom of the cooling coil and the water in the sump. The tube bundles and their layout are generally consistent with prior practice for the purposes of maintaining the structural arrangement of the cooling-tower housing footprint. However, the direction of fluid flow through the tubing has been reconfigured to provide the last leg or segment of each circuit with fluid flow in the vertically upward direction. The upward flow in this last leg or segment takes advantage of the above-noted plenum-area cooling effect, or added cooling, provided below the coil assembly. In this cooling coil assembly arrangement, even for a standard coil assembly, the last leg in the coil is upwardly directed in concurrent flow with the flow of air to better utilize the available heat transfer/temperature reduction for the fluid to be cooled, without incurring any increased operating costs above those associated with current unit operating costs. The prior art generally utilizes inlet and outlet headers or manifolds, which facilitate the handling of multiple tubing structures, but it is known that individually piped arrangements could be configured to accommodate the routing of a tube to produce the directional flow required, and this limitation is considered to be included within the teaching of this application and the use of manifolds to more expeditiously accomplish this task.